The production of a uniform and stable homotropic orientation of liquid crystal phases was hitherto technologically quite difficult. Thus, the liquid crystal phase used was doped with surface-active substances, such as lecithins, long-chain aliphatic amines, quaternary ammonium or phosphonium salts or carboxylatochromium complexes (Appl. Phys. Lett 27, 268 (1975). Coating of glass surfaces with the substances mentioned before introduction of the liquid crystal phase was also customary. The uniformity and stability of the resulting homotropic orientation of the liquid crystal phases, however, leaves something to be desired.
Trisalkanolyoxysilanes for producing a homotropic orientation of liquid crystal phases on surfaces are known from German patent application No. P 33 31 515 (U.S. Ser. No. 647,210 of Sept. 4, 1984). However, these compounds have a number of disadvantages. Thus, dark brown by-products which cannot be separated off from the desired trisalkanolyoxysilane are frequently formed during their preparation from acid anhydrides and trichlorosilanes. Products contaminated in this manner are no longer suitable for surface treatment, since they reduce the optical transparency of the carrier material. Hydrolysis of the trisalkanolyoxy compounds on the carrier surface by the process described in No. P 33 31 515 furthermore frequently leads only to low molecular weight hydrolysis products which are volatile with the steam used and thus do not contribute to modification of the surface treated, which results in incomplete or only partial surface orientation of liquid crystal phases applied.